The present invention relates to cardiac stimulation probes to be placed in the heart coronary system for the stimulation of the left ventricle or left atrium by an xe2x80x9cactive implantable medical devicexe2x80x9d, as such devices are defined by the Jun. 20, 1990 directive 90/385/CEE of the Council of the European Communities, and more particularly by a device such as pacemaker, defibrillator and/or cardiovertor, notably a cardiac generator of xe2x80x9cmultisitexe2x80x9d type.
In contrast to the right ventricle, in which it is simple to implant endocardiac probes through the right peripheral venous system, the permanent installation of probes in a left heart cavity involves important operational risks. For example, there is a risk of bubbles passing towards the cerebral vascular system which is located downstream from the left ventricle. For this reason, one chooses in this case a probe to be introduced into the coronary system, with an electrode disposed against the left ventricle, with the probe access into the coronary sinus system being done via the right atrium.
The introduction of such a probe endocardially is a particularly delicate intervention. It is even more delicate when taking into account the fact that the position of stimulation sites is very important within the framework of xe2x80x9cmultisitexe2x80x9d stimulation, in which the left ventricle and right ventricle stimulation sites are preferably as far part as possible, to optimize a resynchronisation of the cardiac cavities.
It is therefore important that this particular type of probe satisfy a certain number of precise criteria.
Firstly, the probe must be relatively rigid so that its distal end can be easily guided towards the entry of the sinus coronary at the time of implantation and introduced therein independent of any differences in morphology from one patient to the next (in certain pathologies, the atrium are sometimes very dilated), and to avoid pressing on the atrial wall.
Secondly, the probe must have a relative flexibility or suppleness, so that after having found the entry to the coronary sinus, and having introduced the distal extremity of the probe therein, the surgeon is able to move the probe easily in the coronary system. But, at the same time, the probe must have a certain rigidity so that the surgeon can push the probe, without too much difficulty, through obstructions, such as valves, and to transmit the surgeon""s push to the distal end of the probe, ensuring that the probe does not form loops in the right atrium.
Thirdly, once the stimulation site is reached, the surgeon must be able to adjust easily the position of the probe (at present, the probe is very often simply wedged in an extremity of the vein) and, when the site is good, maintain the position of the probe regardless of the size of the vein.
Finally, it is desirable to be able to extract the probe at a later time without damaging the veins of the coronary system.
Ideally, all of these functions or characteristics must be present for a majority of surgeons to be able to use the system. In other words, the system must be sufficiently similar to the existing techniques and current practices to be used.
U.S. Pat. No. 5,683,445 refers to a probe of this type, with a unit made up of a probe body and a stylet. The probe body includes including an elastically deformable hollow sheath and is primarily deprived of any rigid elements, and a distal extremity that supports at least one stimulation electrode. The stylet is a removable stylet ready to be introduced inside the sheath of the probe body and moveable therein. The stylet is relatively rigid as compared to the sheath, and is locally plastically deformable. The distal extremity of the probe has, in the absence of stress, two curves formed of two distinct surfaces. The first surface corresponds to an orientation curve defined by a probe body preform. The second surface corresponds to a support curve defined by a naturally bent form of the probe distal extremity.
This probe construction, however, is not optimal in the field of electric stimulation. Indeed, the hemispherical end carrying the electrode ensures, because of its axial symmetry, an identical placement of the active surface against the myocardium, regardless of the orientation of the probe extremity. But, because of the hemispherical end, this probe structure presents several serious disadvantages, in particular, a risk of parasitic stimulation of the nerves by the electric stimulus, and a low current density, and therefore a relatively lower physiological effectiveness and larger consumption of energy.
It is, therefore, an object of the present invention to cure the aforementioned disadvantages, by proposing an improvement of probe of the type generally taught by U.S. Pat. No. 5,683,445, which is optimised for electrical stimulation.
To this end, the present invention is directed to providing a probe having a distal extremity which has an elbow and is self-directional (auto-orienting) during installation. The probe has an electrode which is a sectoral electrode, having an active surface portion on the side of the probe extending, in a radial plane, only on one sector of the probe body. The sectoral electrode active surface is preferentially turned in a direction that is appreciably perpendicular to a plane formed by the elbow of the probe body distal extremity and protrudes from the surface of the probe body in a radial plane similar to the curve of the probe body distal extremity.
In accordance with a preferred embodiment, the removable stylet has a distal extremity which is provided with a ball at its distal end. The stylet preferably comprises a core having a distal portion and a proximal portion, and a reinforcement tube over the core such that the core is sheathed over its proximal portion by the reinforcement tube, which increases the rigidity of the stylet proximal portion. The stylet core emerges from the reinforcement tube at the distal part, and the distal part thus has a relatively greater flexibility.
In one embodiment, the probe body distal extremity comprises an axial passageway which is maintained sealed closed in the absence of an external or interior stress on the axial passageway, and which has an opened condition which allows a small stylet, more particularly an angioplasty stylet, to penetrate and pass through the axial passageway and so to extend beyond the probe body distal extremity. This occurs when the angioplasty stylet is substituted for the stylet initially introduced into the probe body, as discussed below.
In another embodiment, the probe body distal extremity comprises an elastic system that is resiliently urged against the inner vein wall. The elastic system is positioned on the distal extremity diametrically opposite to the active surface of the electrode, and thus aids in maintaining the electrode active surface in conducting contact with the myocardium wall. Preferably, the elastic system is a counter-elbow, also extending in a plane approximately perpendicular to the plane formed by the elbow of the probe distal extremity. Alternately or in addition, the elastic system can be one or more elastically deformable bodies projecting from the probe surface, which bodies are interposed between the inside of the external wall of the vein and surface of the myocardium.